The exemplary embodiments are directed to a machine or process that is subject to periodic or occasional maintenance or service.
The related art includes machines, such as, for example, a copier, a printer, or the like that are under a closed-loop feedback control. If a machine is subject to occasional or periodic maintenance or service, the effect of the maintenance or service may change the machine and/or the control process of the machine. Such maintenance or service may include cleaning, repair, part replacement, or the like. A change to the machine due to maintenance can have a large impact on the machine response and hence the closed-loop behavior of the system. For example, under closed-loop control, the machine inputs may be at certain values in order to keep machine performance on target, and the values for the machine inputs required prior to maintenance may be different from the values required after maintenance.
For example, in the related art, there is an on-line process for cleaning donor rolls and wires in the Hybrid Scavengeless Development (HSD) subsystem of an imaging device, known as Vdm blip. This process involves periodically reversing a bias on the donor rolls with respect to the voltage on the magnetic roll while maintaining a nominal wire voltage waveform. This approach electrostatically cleans the donor rolls by developing the toner from the donor rolls back onto a magnetic roll, and results in the wires scrubbing against the donor rolls, further aiding the cleaning process. See, for example, U.S. Patent Publication No. 20050095024, hereby incorporated by reference in its entirety.
This on-line cleaning process was implemented on a xerographic printer where it was demonstrated that periodic donor roll and wire cleaning leads to a large improvement in toner life. However, this cleaning process may interact with existing xerographic process controls, such as the process controls described in, for example, U.S. Pat. No. 5,471,313, hereby incorporated by reference in its entirety. This interaction may cause the developed toner mass per unit area (DMA) to temporarily deviate from a predetermined target value. This interaction comes about because after the cleaning process, developability is enhanced such that relatively small process control actuator values are required to meet the DMA target. Existing process controls are not aware of this sudden change in developability, and, as a result, after the cleaning process the existing process controls use actuator values that are too large to meet the DMA target. Subsequent to the cleaning process, the existing process controls observe deviations in the measured DMA and adjust the actuator values in order to bring DMA back on target. The problem is that color shifts are observed in images as the process controls readjust to the new developability state. Furthermore, the time it takes for the machine or system to return to a steady state indicates the significance of machine transients that occur during maintenance. Thus, this on-line cleaning process was subsequently eliminated as a means of improving toner life, in large part because of the DMA transients.